In a trench gate type semiconductor device, an excessive electric field concentration occurring at a bottom portion of a trench type insulated gate results in destruction of the semiconductor device. In order to prevent an electric field concentration, for example, Japanese Patent Application Publication No. H9-82954 (Patent Document 1) and Japanese Patent Application Publication No. 2003-174166 (Patent Document 2) describe setting a depth of a trench of an insulated gate at an outermost periphery of an actual operation region shallower than a depth of a trench of another insulated gate in the actual operation region. In addition, Japanese Patent Application Publication No. 2004-158680 (Patent Document 3) describes setting a depth of a trench of an insulated gate at an outermost periphery of an actual operation region deeper than a depth of a trench of another insulated gate in the actual operation region. In these conventional techniques, trenches of the respective insulated gates have a uniform depth in a longitudinal direction.